A conventional bicycle frame is composed of a head tube, a seat tube, a down tube, a seat stay and a chain stay.
That is, the head tube is connected to a steering handle connector at an upper end thereof, and connected to a front wheel rotation connector at a lower end thereof. The seat tube is connected to a saddle connector at an upper end thereof and connected to a chain driver, or crankset, at a lower end thereof.
The top tube and the down tube connect the head tube and the seat tube to support these elements, and the seat stay and the chain stay connect a rear wheel rotation connector and the seat tube to support these elements.
Recently, bicycle frames have been made through stamping forming of left and right panels and then bonding the panels. In the stamping frame, one drawback is the increase in production costs in order to produce various sizes of frames.
Therefore, research for reducing production costs has facilitated making a front triangle portion (front frame) using a mold and making a rear triangle portion (rear frame) in one size for common use.
Furthermore, since correction operations for keeping the angle between the left and right stays constant due to thermal deformation in the bonding portion of the stamping frames may be performed, productivity may be reduced.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.